1. Field of the Invention
The present invention relates to an organic/inorganic composite film, and in particular relates to an organic/inorganic composite film with high transparency.
2. Description of the Related Art
An organic/inorganic composite material is a new type of material which has both the advantages of organic and inorganic materials. Typically, inorganic materials such as glass, fibers, clay, or carbon black are added to a polymer as a supporting or strengthening agent, such that the physical properties of the polymer are enhanced. However, in addition to the strengthening performance, the original properties of the polymer are influenced by the dispersity and the particle size of the inorganic materials.
In various fluoride resins, poly(vinylidene fluoride) (PVDF) has the best mechanical strength and provides good strength in high temperature and pressure environments. Moreover, PVDF has good tenacity, hardness, abrasive resistance, anti-UV properties and weather aging resistance as well as good chemical and thermal stability. Meanwhile, PVDF is easy to be processed and has excellent applicability. Typically, a composite material formed by adding clay into the PVDF polymer may have advantages such as: 1. good piezoelectric characteristics; 2. good mechanical properties; 3. a low expansion coefficient; 4. high thermal resistance; 5. hydrophobic properties; 6. good permeability; and 7. good aging resistance. PVDF has three main crystalline phases, namely α, β and γ. The α crystalline phase is most seen, and the γ crystalline phase is a mixture of the α crystalline phase and the β crystalline phase. Among them, the β crystalline phase has the best piezoelectric characteristics and mechanical properties. In general situations, the β crystalline phase cannot be directly obtained from the melt of the PVDF, and only can be solidly transformed from the α crystalline phase.
Typically, a PVDF/clay composite material is formed by melting and mixing the PVDF and clay. The addition of the clay will result in a phase transformation of the PVDF. For example, the α crystalline phase of the PVDF will be transformed to the β crystalline phase, such that the piezoelectric characteristics and mechanical properties of the PVDF are enhanced. However, the PVDF/clay composite film formed by the above method may have poor optical properties and the clay content is only 5-10 wt %.
Furthermore, in another conventional method, the PVDF composite material is formed by mixing polymethylmethacrylate (PMMA) and PVDF. The optical properties of the PMMA/PVDF composite film can be improved by this method, because the PMMA is transparent. However, the PMMA/PVDF composite film does not have the physical properties of organic/inorganic composite films since there is no incorporation of inorganic materials. Furthermore, the transparency of the PMMA/PVDF composite film depends on the content of the PMMA. The lower the PMMA content is, the lower the transparency of the PMMA/PVDF composite film may be obtained.
Thus, a novel PVDF/clay composite material with excellent optical properties is needed to be developed.